Radio frequency (RF) catheter ablation is an established treatment for patients with cardiac arrhythmias. RF ablation of atrio-ventricular nodal reentrant arrhythmias has been highly successful, since the known anatomy of the atrio-ventricular node enables precise identification of the site of origin of the arrhythmia and thus delivery of the ablative energy. Ablation of ventricular tachycardia (VT) presents a greater challenge, since the origin of the arrhythmia could be anywhere in the ventricles, and existing techniques used to locate the site usually require that patients be maintained in arrhythmia for a significant period of time. These factors combine to limit the procedure primarily to treatment of slow VTs in patients who are hemodynamically stable during arrhythmia. In Phase I of this Fast-Track project, concept feasibility will be demonstrated for a new catheter guidance system that will direct the tip of an ablation catheter to the site of origin of an arrhythmia and reduce the time needed to locate the site such that a patient need only be maintained in the arrhythmia for a few beats. The system will feature an innovative "inverse algorithm" analysis code that uses a single equivalent moving dipole (SEMD) to model both electrocardiograph (EGG) potentials from body-surface electrodes and the current pulses delivered from the tip of an ablation catheter. By processing body surface potentials during a few beats of VT, the system will identify the SEMD location that corresponds to the source of the arrhythmia when the bioelectrical source is most localized. Using the same algorithm, it will then identify, in real time, the location of the catheter tip from analysis of potentials resulting from low-energy dipolar current pulses delivered to electrodes located at the tip. The system will also include a real-time graphical display that will allow a clinician to quickly guide the catheter tip to the source of the arrhythmia for precise delivery of RF energy. Even in the presence of realistic levels of noise in the ECG signals, preliminary work has shown that estimation of the SEMD location from body surface potentials is a breakthrough innovation that will allow for precise, rapid guidance of ablation catheters to arrhythmic foci. Phase I will prove feasibility in a breadboard system developed to demonstrate the ability to guide an ablation catheter to the location of an electrical source within a phantom torso. This work will serve as the foundation for development and in-vivo test of a full prototype guidance system in Phase II.